1. Field of the Invention
The present invention relates to a fluorescent lamp lighting apparatus, and more particularly, to a fluorescent lamp lighting apparatus using an inverter circuit.
2. Description of the Related Art
Generally, any conventional apparatus for lighting an electric discharge lamp like a fluorescent lamp for example uses an inverter circuit. For example, a typical conventional fluorescent lamp lighting apparatus has the structure described below. The positive electrode of DC power source is connected to the drain of the first field-effect transistor, whereas the negative electrode of this DC power source is connected to the source of the second field-effect transistor. The source of the first field-effect transistor is connected to the drain of the second field-effect transistor and also to an end of the primary coil of a leakage transformer. The other end of this primary coil is connected to a contact between the first and second capacitors which are connected in series between both ends of the DC power source. Furthermore, one ends of filaments on both sides of a fluorescent lamp are connected to both ends of the secondary coil of this leakage transformer. The other ends of these filaments are connected to such portions slightly inside of the both ends of the secondary coil. A startup capacitor is connected in parallel between the other sides of these filaments.
Assume that the first and second field-effect transistors of the lighting apparatus having the above structure are alternately turned ON and OFF. Then, DC voltage delivered from the DC power source is converted into AC voltage to induce alternate current on the part of the secondary coil of the leakage transformer before eventually lighting up the fluorescent lamp. Nevertheless, this conventional fluorescent lamp lighting apparatus magnifies resonant current when no load is present in the apparatus. This in turn causes the first and second field-effect transistors to incur unwanted destruction in some cases. To prevent this, all the conventional fluorescent lamp light apparatuses need to install an independent safety circuit. To prevent these field-effect transistors from incurring unwanted destruction, there is such a conventional electric-discharge lamp lighting apparatus having a typical structure described below.
The positive electrode of the DC power source is connected to the drain side of the first field-effect transistor having the source connected to the drain of the second field-effect transistor. The negative electrode of this DC power source is connected to the source of the second field-effect transistor. The first and second capacitors are connected to each other in series, which are respectively connected between both ends of the DC power source. An end of one of filaments of a fluorescent lamp is connected to the contact between the first and second field-effect transistors via a reactor. An end of the other filament of this fluorescent lamp is connected to the contact between the first and second capacitors. A startup capacitor is connected between the other end of one of these filaments and the other end of the other filaments.
The first and second field-effect transistors of the fluorescent lamp lighting apparatus having the above structure are alternately turned ON and OFF to convert DC voltage into the predetermined AC voltage so that the fluorescent lamp can be lit up. While the fluorescent lamp is not loaded in the lighting apparatus, circuits of this lighting apparatus remain open and inoperative so that the first and second field-effect transistors can be prevented from incurring unwanted destruction while no load is present.
Nevertheless, there is no means of insulating the fluorescent lamp itself from the DC power supply source, and thus, there is potential fear to incur electric shock while loading and unloading the fluorescent lamp.